Power amplifier

Abstract

A power amplifier includes a class A power amplifier and a class B power amplifier driven by the same input signal. The class A amplifier includes a pair of load driving power amplifying elements, and a further pair of amplifying elements serves to drive the power amplifying elements. To obtain good operating characteristics and reduce distortion, the further pair of elements are powered by power supplies for the class B amplifier.

What is claimed is: 
     
       1. A power amplifier comprising: a class A power amplifier circuit including a pair of power amplifying elements having power supply terminals and output terminals wherein said power amplifying elements drive a load connected to said output terminals in response to control signals, amplifying elements serving as drivers for said power amplifying elements wherein said amplifying elements provide said control signals to said power amplifying elements, a voltage source connected between said power supply terminals of said power amplifying elements, and a voltage amplifying stage for receiving an input signal and for supplying an amplified output signal to said amplifying elements, said amplifying elements providing said control signals to said power amplifying elements in accordance with said amplified output signal;   a class B amplifier circuit drivable by said input signal supplied to said voltage amplifying stage and including a pair of output amplifying elements arranged in a push-pull connection and having at least one output connected to said voltage source; and   a power supply connected to supply operating power to said output amplifying elements and to said amplifying elements.   
     
     
       2. A power amplifier as claimed in claim 1, said class A power amplifier circuit being supplied with power from power supplies of relatively small capacity with respect to those of said class B amplifier circuit. 
     
     
       3. A power amplifier as claimed in claim 1, said voltage source comprising a single source connected between said supply terminals, a pair of resistors being arranged in parallel with said single source, and a midpoint of said resistors being fed back to an input of said class B amplifier circuit. 
     
     
       4. A power amplifier as claimed in claim 1, said voltage source comprising a pair of floating sources connected in series, an output of said class B amplifier circuit being connected between said floating sources. 
     
     
       5. A power amplifier as claimed in claim 4, said pair of output amplifying devices being arranged in a single ended push-pull fashion.